Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Earnings Per Share [Abstract]
Net income available to common stockholders	$ 33,849	$ 22,875	$ 53,512	$ 33,585
Weighted average common shares outstanding, basic (in shares)	48,017,000	47,969,000	48,007,000	47,949,000
Dilutive SARs (treasury method) (in shares)	0	0	0	3,000
Weighed average common shares outstanding, dilutive (in shares)	48,017,000	47,969,000	48,007,000	47,952,000
Earnings per share - basic (in dollars per share)	$ 0.70	$ 0.48	$ 1.11	$ 0.70
Earnings per share - diluted (in dollars per share)	$ 0.70	$ 0.48	$ 1.11	$ 0.70
Net Income Per Share Calculations
Dilutive SARs (treasury method) (in shares)	0	0	0	3,000
Stock Appreciation Rights (SARs)
Earnings Per Share [Abstract]
Dilutive SARs (treasury method) (in shares)			0	0
Net Income Per Share Calculations
Dilutive SARs (treasury method) (in shares)			0	0